You can bring .jpg, .png, etc images onto the timeline in Vegas just as you would video clips.

if you have say 50 photos located in one folder, select them all and you can drag them all at once onto the Vegas timeline. Add music to an audio track below and there you go. Use the pan and crop feature to add motion to your photos.

Use Ultimate S plugin to automatically do all sorts of cools things to your slideshow like match your clips or photos to the length of the music you use.

There's also several free scripts out there that will export PNG or JPG images from the timeline in a variety of ways. If you want to just copy the current cursor location, there's another script here:http://www.jetdv.com/scripts/SnapshotToFile.js

You can also do it manually. Change the preview to Best (Full) and then click on the little "disc" icon above the preview screen.